Reaction of laser-ablated Fe atoms with oxygen molecules in a condensing argon stream produced FeO, FeO2, FeO3, FeO4, Fe2O, Fe2O2, and Fe2O4 molecules, which are identified from oxygen isotopic shifts and multiplets in matrix infrared spectra. The Fe + O2 reaction gives symmetrical bent, symmetrical cyclic, and asymmetrical bent FeO2 isomeric products with triplet, triplet, and quartet isotopic absorptions, respectively, using statistically mixed 16,18O2 as the reagent. The major reaction product symmetrical bent OFeO iron dioxide molecule (150 ± 10°) is characterized by stretching fundamentals at 945.8 and 797.1 cm-1, and the asymmetric bent FeOO form exhibits a 1204.5 cm-1 absorption. The cyclic isomer Fe(O2) produced spontaneously during annealing in solid argon absorbs at 956.0 cm-1. Oxygen and iron isotopic absorptions show that FeOFe is a symmetrical bent (140 ± 10°) molecule. Rhombic Fe2O2 absorbs at 517.4 cm-1. Evidence is presented for isomers of FeO3, FeO4, and Fe2O4. Density functional theory was used to calculate energies, structures, and frequencies for product molecules to support their identification.